1. Field of the Invention
This invention relates to an improvement in a grapple attachment for log loader for use in carrying out logs or lumbers.
2. Description of the Prior Art
Conventional grapple attachments for log loader basically comprise a main frame connected to a driving arm of a log loader or similar civil engineering machine, a pair of tines or fork members integrally secured to and extended forwardly from both lateral ends at the lower part of the vertically erected main frame, and a pair of clamp arms pivoted to both lateral ends at the upper part of the main frame such that they are vertically rotated by adequate means, e.g., hydraulic cylinders to and from the tines in order to carry out logs or lumbers clamped between the tines and the clamp arms.
Since most of such conventional grapple attachments for log loader have been intended to carry out logs or lumbers already stacked orderly and transfer them, for instance, in the vertical direction while carrying them on the tines, they have been designed such that the main frame for supporting the tines and the clamp arms has a beam assembly comprising vertical and lateral beams connected to each other in a grid-like structure, and the base end for each of the clamp arms is pivotally received between a biforked axle-bearing bracket disposed to the upper part of the main frame.
As the result, although the grapple attachment of such a conventional design can readily withstand the loads exerted uniformly on the main frame along with the extending directions of the beam such as in the vertical direction, its structural strength is extremely poor against those loads which are exerted locally or at random. Particularly, upon actual use of such a grapple attachment for log loader, for example, in the deforestating field or the like, the grapple attachment is often operated under rather irregular and severe working conditions. For instance, a cut down tree or log is sometimes held between the tine and the clamp arm only on one side of the main frame in a so-called canti-levered manner and dragged out forcibly. This may cause locally concentrated stress or obliquely oriented force to the base of the main frame, thereby possibly resulting in cracks to the main frame at the connections of the beam members thereof, which may readily lead to the structural damages such as deforming of the main frame and undesirable disordering in the parallel positional relationship between the opposing tines and clamp arms. Furthermore, the biforked axle-bearing brackets pivotally receiving the clamp arms, when exposed to such irregular and severe working states, tend to warp outwardly and frequently develop cracks or flexures in these portions.